Dysregulation of cell cycle regulators is a central theme in carcinogenesis. Any stimulus that brings about a change in a cell's proliferation status must impinge upon a cyclin/cyclin-dependent kinase (CDK) complex. DOC-1 is a growth suppressor/putative tumor suppressor identified using a hamster oral cancer model and subtractive hybridization. Ectopic expression of DOC-1 in malignant keratinocytes is associated with suppression of transformation phenotypes in culture. DOC-1 has been shown to associate with DNA polymerase-alpha/primase and CDK2. DOC-1 is a specific inhibitor of CDK2 activity and DNA replication (p 12INK2/DOC-1). By searching NCBI databases, the human DOC-1 sequence was mapped to two human UniGene clusters with one encoding for DOC-1 (Hs.3436) and the other encoding a highly similar protein (Hs.25664), mapped to chromosome 11q13, at interval D115913-D 111S1337, a frequently altered site in human cancers. Sequencing of cDNA clones from Hs.25664 cluster led to the identification of an open reading frame that encodes for a protein of 126 amino acids. Analysis using BLASTP program revealed 57 percent amino acid identity with DOC-1. We name this gene DOC-1R for DOC-1-related. Northern blot analysis using the DOC-1R cDNA probe revealed that DOC-1R is ubiquitously expressed in all normal human tissues examined. Data will be shown that DOC-1R associates with CDK2 in vitro and in vivo. We hypothesize that DOC-1R is a regulator of CDK2-mediated cell cycle activities. In addition, its chromosomal location at 11q13 led us to hypothesize that DOC-1R is mutated in human cancers. There are two Specific Aims in this proposal. Specific Aim 1 is to examine the role of DOC-1R in CDK2-mediated cell cycle biology. Specific Aim 2 is to identify DOC-1R mutations in human cancers associated with 11q13 alteration. The long term goal of this proposal is to substantiate the role of DOC-1R as a new CDK2 regulatory protein, in the regulation of CDK2-mediated cell cycle biology in normal and tumor development.